In data processing systems, disc drives are often used as storage devices. Such drives use rigid discs, which are coated with a magnetizable medium for storage of digital information in a plurality of circular, concentric data tracks. The discs are mounted on a spindle motor, which causes the discs to spin and the surfaces of the discs to pass under respective hydrodynamic (e.g. air) bearing disc head sliders. The sliders carry transducers, which write information to and read information from the disc surfaces.
An actuator mechanism moves the sliders from track-to-track across the surfaces of the discs under control of electronic circuitry. The actuator mechanism includes a track accessing arm and a suspension for each head gimbal assembly. The suspension includes a load beam and a gimbal. The load beam provides a load force which forces the slider toward the disc surface. The gimbal is positioned between the slider and the load beam, or is integrated in the load beam, to provide a resilient connection that allows the slider to pitch and roll while following the topography of the disc.
The slider includes a bearing surface, which faces the disc surface. As the disc rotates, the disc drags air under the slider and along the bearing surface in a direction approximately parallel to the tangential velocity of the disc. As the air passes beneath the bearing surface, air compression along the air flow path causes the air pressure between the disc and the bearing surface to increase, which creates a hydrodynamic lifting force that counteracts the load force and causes the slider to lift and fly above or in close proximity to the disc surface.
One type of slider is a “self-loading” air bearing slider, which includes a leading taper (or stepped-taper), a pair of raised side rails, a cavity dam and a subambient pressure cavity. The leading taper is typically lapped or etched onto the end of the slider that is opposite to the recording head. The leading taper pressurizes the air as the air is dragged under the slider by the disc surface. An additional effect of the leading taper is that the pressure distribution under the slider has a first peak near the taper end or “leading edge” due to a high compression angle of the taper or step, and a second peak near the recording end or “trailing edge” due to a low bearing clearance for efficient magnetic recording. This dual-peak pressure distribution results in a bearing with a relatively high pitch stiffness.
The bearing clearance between the slider and the disc surface at the recording head is an important parameter to disc drive performance. As average flying heights continue to be reduced, these decreases in fly height can cause the contact frequency between disc and head to increase. For example, while demand for increasing disc drive recording density has resulted in drastic decreases in head-media spacing (HMS), manufacturing variation-induced HMS loss has been observed to be an increasing source of head/media intermittent contact, especially at sub half-micro inch fly heights. Such intermittent contact can damage the head and/or the disc surface, and can induce vibrations detrimental to the quality of head reading/writing at such low fly heights.
The sliders to which read/write heads are attached typically possess three degrees of freedom (vertical motion, pitch rotation and roll rotation) associated with three applied forces, i.e., pre-load forces and air bearing suction and lift forces. Steady state fly attitude of the entire slider is achieved when these three forces balance each other. Desirably, the fluid bearing underneath the slider maintains a steady state position relative to the media and possesses intrinsic stiffness with respect to its three degrees of freedom, i.e., vertical stiffness, pitch stiffness and roll stiffness. Of large interest for HMS variation, contact stiffness is defined as a vectorial combination of slider pitch stiffness and slider vertical stiffness. Contact stiffness characterizes the vertical stiffness of the slider at the particular location of the pole tip. Contact stiffness is defined as:
  Kc  =      Kp                  Kp        Kz            +              b        2            where Kp, Kz and b are respectively the slider pitch stiffness, slider vertical stiffness and distance between slider pivot point and pole tip.
It has been shown that manufacturing variations, such as variation in pitch static attitude or in pre-load forces, impose undesirable variations on the slider in terms of flight attitude. Increasing pitch stiffness and vertical stiffness of the air bearing results in a larger resistance to these undesirable variations. Increasing stiffness is achieved by generating more suction and lift force per unit area. In other words, low manufacturing sensitivity can be achieved by increasing contact stiffness via increases in suction and lift forces.
However, increased suction forces can cause the contact frequency between disc and head to increase during the performance of known loading and unloading processes. Load/unload technology is a known alternative to contact start/stop technology. In accordance with load/unload technology, a ramp is positioned near the outer disc diameter for engaging the suspension to load and unload the slider to and from the disc surface. During the unload process, when disc rotation is powering down or gradually decreasing to a stop, the slider is rotated toward the outer disc diameter until the suspension engages the ramp, which lifts the suspension and the slider away from the disc surface. The slider is then “parked” on the ramp. In order to lift the slider to the ramp, the slider and associated suspension must overcome the suction force, which tends to pull the slider closer to the disc. Depending on the strength of the suction force, it is possible that the slider, on occasion, might slap against the disc surface and cause undesirable head/media contact during the unload process. Generally, as the suction force increases, the likelihood of this type of undesirable contact also increases.
During the load process, when disc rotation is powering up or gradually accelerating to an operational speed, the slider is moved off the ramp and onto the disc. As the slider approaches the disc, a positive air bearing pressure is developed to cushion the slider. However, if this lifting force is developed slower than the suction force (in a negative pressure air bearing design), the slider will contact the disc, which can lead to severe disc/media damage. Also, due to the inconsistencies associated with manufacturing tolerances, sliders with non-nominal pitch static attitude (PSA) and/or roll static attitude (RSA) exist. These unfavorable conditions increase the chances of slider contact with the disc during load/unload processes.
Suction force therefore plays an important role in load/unload contact. While the likelihood of slider contact could be decreased or eliminated by decreasing the suction force, this suction force is needed to maintain high stiffness and low fly sensitivity.
Sliders that provide a solution to this and other problems, and offer advantages over the prior art are therefore desired.